Wide-range loudspeaker



Sept. 24, 1968 N. BISHOP 3,4 5

WIDE-RANGE LOUDSPEAKER Filed marh'l v, 1965 2 Sheets-Sheet 1 INVENTOR.7157 c? NATHANIEL BISHOP Sept. 24, 1968 N. BISHOP 3,

WIDE-RANGE LOUDSPEAKER Filed March '17, 1965 2 Sheets-Sheet 2 INVENTOR.NATHANIEL BISHOP ATTOR/VEVI United States Patent 3,403,235 WIDE-RANGELO'UDSPEAKER Nathaniel Bishop, Fairfield, Conn., assiguor to Newmarkets,Inc., Fairfield, Conn., a corporation of Connecticut Filed Mar. 17,1965, Ser. No. 440,373 Claims. (Cl. 179115.5)

ABSTRACT OF THE DISCLOSURE A loudspeaker capable of reproducing a widerange of audible frequencies and having a low deviation from levelresponse is disclosed. The loudspeaker of the invention can beeffectively operated in an enclosing structure only slightly larger thanthe loudspeaker itself. The disclosed loudspeaker includes a member,associated with the speaker cone suspension means, extending over andcovering the larger end of the speaker cone. This covering member istransparent to sound emanating from the speaker cone and,advantageously, has friction loss damping characteristics and can, ifdesired provide a low frequency barrier between the front and back ofthe speaker cone.

The present invention relates to loudspeakers and is directed morespecifically to improvements in the construction of loudspeakers wherebythe frequency response of a loudspeaker of given size may be effectivelyextended on the low frequency end of the range and the smoothness ofresponse throughout the attainable range is increased.

In conventional sound reproduction systems it is customary to utilize aplurality of speaker units, usually including a high frequency tweeterunit and low frequency woofer unit. The use of two speaker unitsnaturally increases the size and cost, and at least the woofer unittypically is of relatively large size, such that a completewoofer-tweeter unit may represent a physically bulky and unsightly itemof household furniture. In addition, the typical, conventional system,consisting of more than one speaker unit for a given channel, mayrepresent a significant item of expense in a reproduction system.

Although it may be desirable to utilize relatively large size speakerunits for achieving high power levels of bass response, it is more oftenthe case of a typical household hi-fi reproduction system that separatetweeter and woofer speaker units are required because of the relativeinability of a single speaker to deliver with flat response over theentire hi-fi frequency ranges. It is thus one of the basic objectives ofthe present invention to provide a novel and improved speaker system,incorporating a single speaker unit, which is so constructed as todeliver a very flat response over an extended range of frequencies. Withthe speaker of the invention, a hi-fi system of adequate household levelcan be achieved using a single 3 /2 or 4 /2 inch speaker, and because ofthe advantages realized by the novel design of the invention, thespeaker can, if desired, be housed in a small cubic closure. Among otherthings, this enables individual hi-fi speaker systems to be manufacturedin such small sizes as to be readily concealable, or at least able to beunobtrusively placed, in the room.

I have been able to confirm that a remarkably level responsecharacteristic is obtainable over a range of frequencies far in excessof conventional design standards if certain design parameters arefollowed. To some degree, these design parameters are known in theory,but their realization in a single unit speaker of practical, economicaldesign has been elusive. Primarily, a flat response speaker mustincorporate a minimum movable mass, represented by a rigid speaker coneand voice coil, in conjunction with a supporting means for the mass ofhigh enough compliance in the direction of movement of the cone. Inaddition, I have established that, to attain the desired compliance andlow free space resonance in a small and light cone-voice coil structure,the suspension means must be limited to one plane at right angles to theaxis to the cone and voice coil, preferably at the outer periphery ofthe cone. The material or arrangement of materials utilized forsuspension should be increasingly absorptive of cone surface vibrationswith increasing frequencies and, when taken together with the speakercone and voice coil, must have a free space resonance well below thelower limit of the desired response range. The structure must providefor opacity to low frequency pressure differences between the front andrear surfaces of the speaker cone. If the cone is suspended from anannular margin outward to the frame, the necessary opacity may bederived from the suspension material itself. But if the cone issuspended from an annular margin inward to the cone axis, in accordancewith another aspect of the invention, then the suspension material must,of course, be transparent to pressure differences.

In addition to having the characteristics mentioned above, a practical,economical single unit speaker system must utilize components availableon an economical basis and must be capable of controlled production andassembly. To this end, the speaker of the invention incorporates manyspeaker components of essentially conventional design and construction.By way of example, in the practice of the invention it is feasible toutilize a speaker substantially in accordance with the Model P5V3speaker manufactured by Jensen Manufacturing Company, makingmodifications therein with respect to the suspension of the speakercone. The advantageous results of the invention may be achieved, usingsuch conventional speaker components, by eliminating altogether thecustomary suspension facilities for the small end of the cone andreconstructing the suspension facilities for the large end of the conein accordance with the principles of the invention. In particular, theouter edge of the otherwise relatively soft, pliable paper cone isrigidified by means of a light, annular reinforcing element, and thereinforced cone edge is connected to the speaker frame, surrounding orwithin the cone, by high compliance sus-. pension elements having thecharacteristics mentioned above. Reinforcement of the suspension planeof the cone is important, inasmuch as, according to the invention, boththe speaker cone and the compliant suspension elements are of adistortable nature, and the reinforcement serves to isolate the coneitself from the distorting forces applied by the suspension elements andvice versa, and thereby prevent distortion of the cone and of the voicecoil carried thereby.

Pursuant to one aspect of the invention, suspension arrangements areprovided for the speaker cone which, in addition to affording superioraxial compliance, serve to introduce friction-loss damping of nodalvibrations within the cone, which tends to occur at higher frequenciesand normally causes sharp changes in response. This combination providesmaximum flatness of response over the operative range of the system.

In one specific physical embodiment of the invention, the speaker issupported by compliant means extending radially outward to the cone froma fixed support within the cone envelope. This arrangement isadvantageous for the reason, among others, that a relatively largesuspension radius is available in a speaker of small size. Thesuspension material is relatively transparent to the pressure variationsproduced by cone vibration, but includes friction-loss dampingcharacteristics for improving flatness of response.

For a better understanding of the invention, reference should be made tothe following detailed description and to the .accompanying drawing, inwhich:

FIG. 1 is a front perspective view of a speaker system incorporatingprinciples of the invention;

FIG. 2 is a cross-sectional view, taken generally along line 2-2 of FIG.1;

FIG. 3 is an enlarged, fragmentary, cross-sectional view taken generallyalong line 3-3 of FIG. 1;

FIG. 4 is an enlarged, fragmentary, cross-sectional view of a secondmodified form of theinvention;

FIG. 5 is a fragmentary, cross-sectional view of a third modified formof the invention; and

FIG. 6 is a fragmentary, cross-sectional view of a fourth modified formof the invention.

Referring now to the drawing, and initially to FIGS. 1-3 thereof, thereference numeral 10 designates a housing or enclosure for the speakerunit, which may be of cubic form. In keeping with the objective ofminimizing the physical bulk of the system, the housing 10 is designedto have minim-um dimensions in relation to the electromechanicalcharacteristics of the speaker unit itself. As shown in FIG. 2, thefront of the housing 10 is open and receives a speaker unit, generallydesignated by the reference numeral 1.1, of a type incorporatingfeatures of the invention.

The speaker unit 11 includes a flat mounting flange 12, which issomewhat greater in its principal dimensions than the size of the frontopening of the housing 10 and is arranged to be secured to the housingas by means of screws 13. A speaker frame 14, of more or less conicalconfiguration, is adjustably or permanently secured to the back surfaceof the mounting flange 12, by suitable fasteners 15. Typically, thefasteners 15 may provide a permanent connection between the flange 12and the frame 14, although it may be desirable in some cases to providefor limited adjustment of the frame .14, in the plane of the flange 12,for optimizing alignment between relatively movable parts of thespeaker, as will appear.

In accordance with conventional speaker construction, the back portion16 of the speaker frame mounts an annular permanent magnet 17 and anaxially projecting pole piece 18 disposed concentrically within themagnet 17. The magnet 17 and pole piece 18 form a narrow cylindrical airgap 19, as indicated in FIG. 2.

In a low cost speaker of conventional construction, it is customary toprovide a speaker cone 20, formed of a light paper material.conventionally, the cone 20 is suitably suspended from the speakerflange 12 by an integral cone flange formed of the paper material of thecone itself and joined to the main body of the cone by an annularflexible region. In addition, conventional constructions usually includemeans for supporting the inner or small end of the cone. In accordancewith the invention, however, these conventional suspension facilitieshave been replaced by advantageous and improved arrangements accordingto the invention, to be described.

At the center of the speaker cone 20 there is mounted, in accordancewith conventional practice, a cylindrical element 21, which projectsrearward of the speaker cone and concentrically into the annular air gap19. Adjacent its rearward end, the cylindrical element 21 mounts a smallcoil 22, referred to as a voice coil, which is more or less centrallypositioned with respect to the axial end limits of the air gap.

As is well known, actuation of the speaker, to produce audible sounds,is effected by electrical energization of the voice coil 22 with audiofrequency currents in such a way as to cause the speaker cone 20 to moveaxially in a direction determined by the direction of current flow inthe voice coil. For energization of the coil 22, suitable lead-inconductors 23 connect the voice coil 22 with a terminal block 24 on thespeaker frame.

In order to achieve faithful conversion or transduction of audiofrequency electrical signals into audible sounds,

however, it is necessary that the speaker cone 20 respond faithfully tothe energizations of the voice coil 22. In accordance with the presentstate of the art, it is not yet known how to achieve wide-range,faithful audio reproduction in a single cone speaker unit, and in atypical high fidelity system it is conventional to employ at least twoand sometimes a larger number of speaker cones, each optimized to .agiven frequency range. The construction of the present invention,however, enables the faithful response range of a given speaker assemblyto be significantly increased and affords more uniform speaker responsewithin the limits of the increased range, such that, in any case,speaker performance is significantly improved and, for at least somenon-professional high fidelity reproduction systems, it may be feasibleto utilize a single speaker cone according to the invention in place ofthe customary plurality of speaker cones without noticeable reduction inthe quality of sound reproduction. It should be realized, however, thatthe advantages of the unique loudspeaker design outlined herein are notlimited to use in a small single speaker system but may be applied toadvantage in speakers of larger size or smaller size for use in awide-range loudspeaker system suitable for high acoustic level usage.

The improved performance characteristics of the speaker of the invention.are realized by observing the following conditions in the specificdesign of the speaker structure: First, the combined mass of the papercone and voice coil assembly must be maintained as low as is compatiblewith minimum required cone rigidity; second, the suspension of the papercone and voice coil assembly must be limited to one plane of suspensionat right angles to the axis of the voice coil, .and in the smaller sizecones this plane is preferably the plane of the outer edge of the cone;third, provision must be made for rigidifying the pliable cone materialin the plane of suspension; fourth, the material used for conesuspension must have such compliance characteristics that, whenresonated with the mass of the cone and voice coil assembly, it providesa free space resonance substantially lower than the lower limit of thedesired range of acoustical response; finally, the suspension system,or, if the cone is suspended from within its envelope, other facilities,must be so arranged in relation to the frame and housing elements as toprovide opacity to low-frequency pressure differences between the frontand rear surfaces of the paper cone as well as to provide for absorptioncharacteristics with respect to nodal cone vibrations at increasingfrequencies.

In accordance with the above conditions, the illustrated speakerassembly of the invention omits the customary small end cone suspensionand provides for supporting of the paper cone 20 solely by its outerflange. A compliant cone supporting material, which I have found to bevery advantageous in satisfying the above-mentioned conditions, is asoft chamois, felt, or pliable plastic foam material. In accordance withone specific aspect of the invention, arcuate segments 27 of thesuspension material disposed in a circumferential array about the outeredge of the speaker cone 20. The outer edges of the segments 27 aresecured to the front surface of the mounting flange 12, by suitablecement or by clamping means, and the inner portions of the segmentproject radially inward into overlying relation with and are secured,through a reinforcing ring element to be described, to the outermostextremities of the paper speaker COne 20. The suspension elements 27,which may be on the order of 20 mils in thickness, have particularlydesirable compliance characteristics with respect to movement of thefree inner ends of the element in the direction of the speaker cone axiswhile, on the other hand, the compliance in the plane of the mountingflange 12 is very low, so that the speaker cone and voice coil assemblycan be supported and positioned within the air gap 19 in a reliablyprecise manner.

In accordance with one of the specific aspects of the invention, thepaper cone 20 may be formed of conventional coneforming paper materials,which are relatively soft and distortable. Accordingly, in order tosupport and precisely locate the voice coil 22, the outer edge flange 28of the paper cone is reinforced and rigidified, advantageously by beingcemented to a reinforcing ring 29 formed of a light, stiff material,such as kraft paper or the like, which serves to rigidify the circularoutline of the flange 28 and retain its fiat, planar condition underservice conditions. Alternatively, such reinforcement can become aspecification of cone fabrication wherein the normal complaint annularring of thin paper deposit would be supplanted by a thick depositproviding the desired rigidity. The suspension elements 27 have theirprojecting inner ends cemented to the reinforcing ring 29, substantiallyas shown in FIGS. 2 and 3, so that the soft, flexible paper cone 20' isisolated from suspension forces which might otherwise tend to distortthe configuration of the cone, particularly in view of the cantileversuspension thereof.

As shown in FIGS. 1 and 2, the arrangement and disposition of thechamois suspension elements 27 is such as to form a relatively completebarrier between the front and back sides of the cone 20, to provide forrelative opacity to low frequency pressures. In addition, the soft,pliable, absorbent nature of the chamois is such that it serves toabsorb vibrations in the higher frequency ranges, with increasingeffectiveness as the frequency increases, to provide for a more levelresponse over the operative range of the speaker.

It should be clearly understood, of course, that material other thanchamois may be used in the formation of the suspension elements 27,although chamois has been found to be a particularly advantageousmaterial to satisfy the various conditions heretofore mentioned withrespect to extremely high compliance in the axial speaker direction,sound opacity and high frequency absorption characteristics, etc. Feltand styrofoam are examples of other advantageous materials which may besubstituted for chamois.v

In accordance with the invention, high frequency absorption or dampingis obtained by friction loss, so that high frequency energy at specificfrequencies which ordinarily cause peaks in the response of theloudspeaker is actually partly dissipated as heat. If the principalmaterial used for cone suspension does not have suitable friction-lossdamping characteristics, then special friction-loss material must beutilized in addition to the principal suspension material.

A speaker constructed in accordance with the principles described, andas illustrated in FIGS. 1-3, exhibits superior response characteristicswith respect to an otherwise conventional speaker of similarconstruction, incorporating conventional suspension means adjacent thevoice coil and at the outer edge of the cone. Not only is the range ofthe speaker extended, but it exhibits superior flatness of response withits operative range, such that the undesirable distortions of mid-rangepeaking and the like are significantly minimized. The advantages aresuch that an acceptable high fidelity reproduction system may beprovided using a single, relatively small diameter (3.5 inch cone)speaker unit, which is light in weight and can be inconspicuously housedand located. While the power limitations inherent in any small diameterspeaker impose practical limits on the audibility of very lowfrequencies, the speaker according to the present invention, in additionto having an extended low frequency range to begin with, hascharacteristics, probably stemming from its particularly flat responseover its operative range, which impart a desirable and advantageousimpression of low frequency reproduction through clear reproduction ofhigher harmonics of the low frequencies, which of course requires anability to move at the low frequency fundamental.

It is well known in the art of acoustics that the nonlinearcharacteristics of the human ear will recreate a low frequency ifharmonics of this low frequency impinge upon the eardrum. If theharmonics of a pure low frequency tone, say 30' cycles, are not createdby distortion in the amplifier, they will not be created by theloudspeaker unless the cone is able to respond or move significantly atthe fundamental frequency itself. In the speaker of the invention, eventhough the fundamental sound pressure reproduced may be low, at lowfrequencies, the action of the cone serves to produce acoustic harmonicswhich will beat in the ear and thereby recreate the fundamental tone.

Referring now to FIG. 4, there is shown a modified form of the inventionwherein the compliant suspension arrangements for the speaker cone maybe provided by a material which, while having the necessary highcompliance, does not necessarily have adequate friction-loss dampingcharacteristics. In such case, it is contemplated by the invention thatseparate friction-loss damping means will be provided in, or in directassociation with, the suspension arrangements.

In the FIG. 4 modification, the speaker cone 50, suspended only at itsouter edge, may be provided more or less along conventional lines, withan integral annular bellows portion 51, which is designed and/or treatedto be highly compliant and permit axial vibratory movements of the conerelative to a rigid mounting flange 52. In accordance with one aspect ofthe invention, the outer edge portion of the cone 50, just inside itsintegral connection to the compliant bellows portion 51, is rigidifiedto provide a stitf cone rim portion 53 of substantially fixed circularconfiguration and planar form. The necessary rigidity may be imparted bysuitable impregnation or other treatment of the rim or by other means,such as cementing thereto a light, stiff reinforcing ring 54. Howeverthe reinforcement of the cone rim area is carried out, it must beconsistent with maintaining the mass of the cone and its rim as low aspracticable.

In order to provide desired damping of high frequency vibrations, theouter flange 55 of the cone suspension portion is secured to themounting flange 52 through a friction-loss damping element 56, which maybe a ring of a material such as felt, Styrofoam, or the like, which willdissipate vibratory movements as heat, to an increasing extent withincreasing frequencies. This energy absorption minimizes resonant peakswhich otherwise would result from nodal vibrations of the speaker coneand serves to flatten the response of the speaker over its operativerange. It will be understood, of course, that separate friction-lossdamping means are not required where the compliant suspension meansinherently has friction-loss damping characteristics, as in the case offelt, chamois, or like suspension materials.

In the modification of FIG. 5, the suspension means for the speakerextend radially outward to the speaker rim, from a point within thespeaker cone envelope, instead of radially inward from a point outsidethe envelope as in the case of more conventional constructions. In thearrangement of FIG. 5, a mounting flange is secured to the enclosure 10and supports a frame 61 carrying an annular magnet 62 and pole piece 63.A supporting rod 64 projects axially forward from the pole piece 63 andis secured at its forward end, by means of a mounting plate 65 andsuitable fastening nuts 66 to a suspension element 67 which extendsradially outward to the rim of the speaker cone 68. Within the purviewof the invention, the suspension element 67 may be in the form of asolid disk, substantially closing off the open end of the speaker cone,or it may be of spoked configuration. In any event, either byconfiguration or by the composition of the material from which it ismade, the supporting element 67 is transparent to sound vibrationsemanating from the speaker cone 68. Felt or styrofoam are suitablematerials for the purpose, and have additional advantages in that Inaccordance with the invention, the cone 68 of the FIG. 5 modificationhas its rim portion 69 rigidified, as by a reinforcing ring 70, and thesuspension element 67 is secured to the reinforced rim under sufiicientradial tension to support the speaker cone with its voice coil 71accurately aligned in the air gap. The necessary opacity to lowfrequency vibration, between the front and back sides of the speakercone, may be provided by means of a limp annular sealing element 72, offelt or the like, which is connected to the flange 60 and the cone edgebut does not perform a support function or otherwise affect the actionof the cone 68. Alternatively, the seal may be formed by establishing aclose fitting relationship between the outer edge of the suspensionelement 67 and the inner edge of the flange 60 or by providing anobstructing lip (not shown) in line with the gap between the suspensionelement and the mounting flange 60.

The modification of FIG. 6 is similar in principle to the modificationof FIG. 5, except that a suspension element 80 illustrated to be formedof felt, is mounted on the axis of the speaker cone 81 by a mountingbracket 82 secured to the front of th mounting flange 83. The mountingbracket 82 may be of relatively small dimensions, viewed from the frontof the speaker, so as to be relatively non-obstructive to pressuresource propagation from the speaker.

In the modification of FIG. 6, the felt suspension element 80 is securedby a short bolt 84, extending into the cone envelope from the mountingbracket 82. The supporting element extends radially outward into securedrelation with the reinforced outer rim of the speaker cone,substantially as described in connection with FIG. 5. The bolt 84 mayhave a shoulder, where it meets the coneside surface of the bracket 82,and a threaded extension beyond the opposite face of the bracket,engaged by a nut 85. The bracket 82 may have an oversize hole permittingadjustment and locking if required in production. The entire assemblyalso could be welded where manufacturing tolerances permit. If thestructure is s'ufliciently rigid, an inward extension of the bolt 84could be used to support the pole piece within the magnet.

The modifications of FIGS. 5 and 6 incorporate the various inventiveprinciples described with reference to the forms of the inventiondescribed in FIGS. l-3 and have, in addition, certain relativeadvantages with decreasing speaker sizes. In this respect, it isadvantageous to prO- vide a relatively long suspension radius betweenthe point of rigid attachment of the suspension means and the point ofits attachment to the rim of the speaker cone. Where the suspension isfixed along the speaker axis, the effective length of the suspensionmeans approximates the maximum radius of the speaker cone, in an overallinstallation which need not be much larger than the speaker itself. Toachieve a corresponding effective suspension length in a system in whichthe suspension means is radially outward of the speaker cone, theoverall installation would have to be approximately twice the maximummoving mass, rigidified cone edge, and high comof center-outward conesuspension is the ability of such a structure to give the designer widelatitude in the choice of suspension material, radial length of materialused for suspension, and of other design parameters, so as to permit awide designer control over free space resonance of complete cone andsuspension assembly to suit the design requirements.

Speakers of any of the before-described forms are characterized by widerange of response and flatness of response over their operative ranges,while at the same time being of low cost construction. This optimumresult is achieved in part by imparting extremely high axial complianceto the speaker suspension without sacrificing its other operatingcharacteristics. By a combination of minimum moving mass, rigidifiedcone edge, and highly compliance suspension in one plane (that of therigidified cone edge) speaker cone response has been significantlyextended and low frequency resonance reduced well below the lower limitof desired audible response. Although power output of a small speaker isinherently limited at low frequencies, the ability of speakers accordingto the invention to move efliciently and faithfully in response to lowfrequency energizing inputs enables the speaker to respond well and withreasonable output power at harmonics of the low frequency fundamentals.This causes or enables the ear to respond to an effective illusion ofactually hearing the fundamental lows at a reasonable level.

In conjunction with the foregoing, the speaker of the inventionincorporates friction-loss damping means as part of or in conjunctionwith the complaint suspension arrangements, whereby nodal vibrations arepartly dissipated. This provides a built-in mechanical compensation forthe normal tendency of a speaker to peak at certain frequencies withinthe normal range.

A specific feature of the present invention resides in the provision ofmeans, operating in conjunction with highly compliant, single planespeaker cone suspension, for rigidifying the outer edge of the speakercone without adding unduly to its mass. This may be accomplished, whileutilizing a speaker cone of conventional pliable paper material, byproviding an annular rigidifying ring, for example, which is cemented orotherwise incorporated with the outer edge of the cone. Thisarrangement, under service conditions, eliminates dimensional and shapedistortion of the cone and hence the voice coil when subjected to theforces involved in movement of the cone in normal operation. With arigidified low-mass cone, it is possible to utilize suspensionarrangements of extremely high compliance, arranged solely about theouter edge of the cone, while still maintaining proper clearances in theair gap in which the voice coil operates.

While the inventive features described 'herein are applicable toadvantage with large diameter speakers, the more outstanding results arerealized in connection with relatively small diameter speakers, whoserange may be extended with significant improvement in the smoothness ofresponse.

Speakers according to the invention exhibit a flatness of response whichis characteristic only of more costly and sophisticated speaker systemsincorporating conventional principles of construction. In addition, theeffective range of response has been extended, particularly at the lowend.

It should be understood that the specific forms of the invention hereinillustrated and described are intended to be representative only, ascertain changes may be made therein without departing from the clearteachings of the disclosure. Accordingly, reference should be made tothe following appended claims in determining the full scope of theinvention.

I claim:

1. A loudspeaker characterized by a low deviation from level response,which comprises (a) a speaker cone having larger and smaller ends,

(b) a voice coil mounted at the smaller end of the cone,

(c) a supporting frame structure positioned in spaced relation to thespeaker cone,

(d) means serving to rigidify an annular area at the larger end of saidspeaker cone,

(e) radially disposed compliant suspension means connecting saidrigidified annular area with said frame structure,

(f) means forming a relatively sound-opaque barrier between the frontand back of the speaker cone,

(g) friction-loss damping means associated with said speaker cone, and

(h) said suspension means including a highly compliant solid disk-likesuspension element covering the large end of said speaker cone,

(i) said suspension element being transparent to sound vibrationsemanating from said speaker cone.

2. The loudspeaker of claim 1 wherein (a) said suspension element formsa sound barrier between the front and back of said speaker cone that isrelatively opaque to low frequency vibration.

3. The loudspeaker of claim 1 further characterized by (a) saidsuspension element having friction loss damping characteristics therebyminimizing resonant peaks and flattening the response of the speakercone over its operative range.

4. A loudspeaker characterized by a low deviation from level responsecomprising (a) a speaker cone having larger and smaller ends,

(b) means forming a relatively rigid flange area at the larger end ofsaid cone,

(c) a voice coil mounted at the smaller end of the cone,

(d) a voice coil magnet mounted in fixed relation to said voice coil,and

(e) a highly compliant disk-like suspension element secured to saidrigid flange area and substantially covering the larger end of saidspeaker cone,

(f) said suspension element being transparent to sound emanating fromsaid speaker cone and having fric tion loss damping characteristicsthereby minimizing resonant peaks and flattening the response of thespeaker cone over its operative range.

5. The loudspeaker of claim 4 wherein (a) said suspension element formsa barrier between the front and back surfaces of the speaker cone, and

(b) said barrier is substantially opaque to low frequency vibrations.

References Cited UNITED STATES PATENTS 1,861,222 5/1932 Minton 181-311,877,294 9/1932 George 181-31 1,967,223 7/ 1934 Bostwick 181-311,982,443 11/1934 Messick 181-31 2,014,621 9/1935 Jensen 181-312,234,833 3/1941 Preston 181-31 2,897,292 7/1959 Van Den Bosch 179-115.53,138,667 6/1964 Avedon 181-31 KATHLEEN H. CLAFFY, Primary Examiner.

A. A. MCGILL, Assistant Examiner.

U.S. DEPARTMENT OF COMMERCE PATENT OFFICE Washington, 0.0. 20231 UNITEDSTATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,403,235September 24, 1968 Nathaniel Bishop It is certified that error appearsin the above identified patent and that said Letters Patent are herebycorrected as shown below:

Column 4, line 59, after "terial" insert are Column 5, line 3,"coneforming" should read cone-forming line 58, "with" should readwithin Column 7, line 59, "moving mass, rigidified cone edge, and highcom" should read diameter of the speaker cone. A unique advantage line74, "highly" should read high Column 8, line 14, "complaint" should readcompliant Signed and sealed this 9th day of June 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr. E.

Attesting Officer Commissioner of Patents

